It is proposed to study the structural requirements leading to cardioselectivity of the beta-adrenoceptor antagonists. To reach that aim a number of new l-aryloxy-3-arylalkyl-amino-propan-2-ols will be synthesized. Their affinity to Beta 1 and Beta 2 adrenoceptors will be investigated using rat ventricular muscle, rat lung membranes, guinea pig artrial, ventricular and tracheal strips, and in a collaborative effort anesthesized dogs. The obtained data will be compared with the findings of conformational analysis (performed using CAMSEQ-II program) of newly synthesized compounds.